The present invention relates to a support pad for a long hole drill for metal machining with improved properties specially for STS (Single Tube System) system and for drilling tools based on the Ejector® system. The invention also relates to a tool head equipped with a support pad, as well as a method of fabricating such a support pad.
Drilling in metals is divided generally in two types: long hole drilling and short hole drilling. By short hole drilling is meant generally drilling to a depth of up to 3–5 times the drill diameter.
In short hole drilling, the demands are not great, enabling the use of simple helix drills formed either of solid cemented carbide or as solid tool steel or of tool steel provided with cemented carbide inserts.
Long hole drilling, however, puts large demands on good chip formation, lubrication, cooling and chip transport. This is achieved through specially developed drilling systems with specially designed drilling heads fastened to a drill rod and fulfilling the above mentioned demands. The drill head may be of solid cemented carbide but is generally of tool steel provided with a number of cutting inserts of cemented carbide placed in such a way that they together form the necessary cutting edge. In the center of the head, a tough grade of insert is generally used and on the periphery a more wear resistant one. The cutting inserts are brazed or mechanically clamped. Generally the cutting inserts are brazed on small-diameter drills and mechanically secured on larger-diameter drills. In addition, the head is provided with support pads.
Cutting inserts and support pads are made of cemented carbide with various contents of WC, Co and cubic carbides TiC, TaC, NbC depending on the application. Cutting inserts as well support pads are in addition coated with one or more wear resistant layers. Generally, the support pads are coated with a yellow layer of TiN. A long hole drill head with a geometrical configuration of inserts and support pads as outlined above is disclosed in U.S. Pat. No. 6,682,275 the disclosure of which is hereby incorporated by reference.
It is a primary purpose of the invention to provide a support pad and a long hole drill head in combination with such a support pad wherein the useful life and strength is substantially increased, especially when drilling in a titanium-based workpiece.
A second object of the invention is to provide an improved support head and long hole drill head having improved properties for the machining of heat resistant material, titanium based material and cast iron, as well as in the machining of nickel based alloys.